This invention relates to semiconductor power modules, and more specifically relates to a novel module structure which has a smaller part count, can withstand an increased insertion force, and has improved resistance to failure due to vibration and improved thermal performance.
Power modules which provide assemblies of semiconductor devices pre-connected within an insulation housing in various circuit arrangements are well known. A typical module is a Type MB, sold by the International Rectifier Corporation, which is a single phase, full wave bridge-connected device having four internally connected diodes mounted within a square housing, with four copper strap terminals extending from the housing, comprising two a-c and two d-c terminals. The strap terminals are adapted for plug-in connection, if desired, and therefore, have sufficient mechanical strength to enable plug-in. The internal diodes (or other semiconductor devices such as thyristors, power MOSFETs, IGBTs, bipolar transistors, or the like) are mounted in pairs as by soldering to two flat spaced horizontal thin flat copper support plates. Two of the four strap terminals extend integrally from the plate, while the other two terminals are necessarily spaced from the plates. A copper jumper strap extends from the bottom of each of these latter terminals and is soldered to the top of two semiconductor devices, one on each of the plates. Thus, the four terminals define the terminals of a full wave, single phase bridge-connected circuit.
The two terminals spaced from the two bases must extend slightly beyond the edge of the top of the first adjacent semiconductor device chip to which they are connected. Consequently, when the device is plugged into a socket, an insertion force is applied along the length of the terminal, causing a rotational force on the portion which overhangs the edge of the first chip. This insertion force, if too high, will cause the fracture of the chip and failure of the module. These devices are also sensitive to vibration forces for the same reason.
A further problem with the prior art device is that the two connection straps which connect the tops of the semiconductor chips in circuit relation with one another are thin copper straps having central stress relief bends. These straps must have a length equal to that of the center-to-center spacing of the chip. Moreover, they anneal during solder-down and tend to work-harden as the straps flex during temperature cycling.